1) Field of the Invention
A capacitive plate dielectrometer method and system is provided. More particularly, a capacitive plate dielectrometer method and system is provided that is used to measure dielectric properties, such as permittivity, of a test material or sample.
2) Description of Related Art
Methods are known for measuring dielectric properties for design and quality assurance used in the production of bulk absorbing materials, such as materials used in aircraft. Such methods for measuring the material properties use interrogating fields, such as electric, thermal, or acoustic fields. The type of field to be used depends upon the nominal properties of the test material and the condition of interest, such as the depth and location of any features or defects. With regard to dielectric properties, test materials may be classified according to their conductivity or permittivity. Electrical conductivity is a measure of a material's ability to conduct an electric current and is a measure of how well a material accommodates the transport of electric charge. Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium, and it is determined by the ability of a material to polarize in response to the field and thereby reduce the field inside the material. Thus, permittivity relates to a material's ability to transmit or permit an electric field. Permittivity is directly related to electric susceptibility. For example, in a capacitor, an increased permittivity allows the same charge to be stored with a smaller electric field, and thus a smaller voltage, leading to an increased capacitance. In general, permittivity is not a constant, as it can vary with the position in the medium, the frequency of the field applied, humidity, temperature, and other parameters. In a nonlinear medium, the permittivity can depend on the strength of the electric field. Permittivity as a function of frequency can take on real or complex values. Dielectrics are associated with lossless or low-loss materials, and dielectrics are insulators with high permittivity. A given amount of material with high permittivity can store more charge than a material with lower permittivity. To make very high frequency permittivity measurements on test materials that have tensors (a set of quantities that obey certain transformation laws relating the bases in one generalized coordinate system to those of another and involving partial derivative sums, i.e., vectors), such as honeycomb cores, the measurements are typically conducted using rectangular waveguides because of the way the electric fields are oriented. Rectangular waveguide measurements involving frequencies greater than several gigahertz require only a relatively small test sample. However, for lower frequency permittivity testing, waveguide dimensions must become progressively larger. Large waveguide test setup is cumbersome and tedious. Typical large waveguide dimensions may be 48 inches long by 12 inches high by three inches thick in one direction. Moreover, with large waveguides, larger quantities of test materials are required to properly test the material, which can result in possible test sample fabrication difficulties. Low frequency permittivity testing requires large amounts of test material. For example, to test the frequency range from 142 MHz (megahertz) to 242 MHz (megahertz) in a rectangular waveguide, one needs a sample to typically have the dimensions of 48 inches long by 12 inches high by three inches thick in one direction. Use of large quantities of low frequency test materials is expensive and the length of testing is time consuming.
Accordingly, there is a need for an improved capacitive plate dielectrometer method and system for measuring dielectric properties, such as permittivity, of a test material or sample that does not have the problems associated with known devices and methods.